Cellulosic pulps comprising crosslinked xanthate cereal pulps and products made therewith



United States Patent Agriculture 0 No Drawing. Filed Mar. 14, 1962, fier. No. 179,849 13 Claims. (Cl. 162-446) (Granted under Title 35, U.S. ode {1952), sec. 266) A nonexclusive, irrevocable, royalty-free license in the invention herein described, throughout the world for all purposes of the United States Government, with the power to grant sublicenses for such purposes, is herebygranted to the Government of the United States of America.

This invention broadly relates to paper-forming cellulosic pulps containing firmly bonded therewith at least about one percent and up to about 100 percent (based on the dry weight of the celluosic fibers) of a cereal pulp as hereinafter defined that has been formed and coupled 1n situ by crosslinking a Xanthate of a cereal grain product or chemically analogous carbohydrate materials to form therefrom a disulfurdicarbothionate or a multivalent metal dithiocarbonate of the cereal grain or carbohydrate material.

More particularly this invention relates to novel cellulosic pulp compositions and to the products made therefrom, the celluosic fibers of the pulp compositions and subsequently produced paper products having firmly bonded therewith from at least one percent and preferably from about 25 percent to about 100 percent (based on the dry weight of the cellulose fiber) of a crosslinked Xanthate of a cereal grain material such as a cereal flour like whole wheat flour, bran fiour, and refined white flour, a polysaccharide such as starch, cellulose, guar gum, dextran, and dextrin, and a polyhydroxy compound such as sucrose and polyvinyl alcohol.

till more particularly this invention relates to fibrous pulp compositions and to the unexpectedly superior paper or fiberboard products made therefrom in which from only a small amount to substantially half of the normal cellulosic fiber content has been replaced in the furnish prior to sheet formation by adding to the cellulosic fiber furnish in the beater, chest, or other appropriate wet end point an alkali metal solution containing a predetermined proportion of an above mentioned cereal or carbohydrate xanthate and then crosslinking the dispersed native alkali xanthate in situ by means of a conventional oxidizing agent such as iodine, chlorine, or with ions of a polyvalent metal (e.g., those of zinc or ferric iron), to form the corresponding disulfurdicarbothionate or metal dithiocarbonate of the aforesaid cereal grain or related carbohydrate material. For convenience the term cereal pulp will be understood to mean any of the cellulose-replacing crosslinked Xanthatcs comprising the disuliurdicarbothionates or the polyvalent metal dithiocarbonates of starch, ground whole wheat flour, bran fiour, defined white fiour polysaccharide materials, fiour fractions and other natural and synthetic polysaccharides and polyhydiroxy compounds.

This invention also relates to the preparation of pulps yielding improved greaseproof-type paper.

in yet another aspect this invention relates to the surprising discovery that homogenously incorporating a small to large addition of a cereal pulp material as hereinabove defined into a conventional cellulose pulp dispersion ice markedly increases the freeness thereof and greatly facilitates the drainage of water thus permitting the use of more concentrated cellulose pulp dispersions than heretofore with attendant reductions in water consumption, production time, and power.

Xanthated starch per se is well known as pointed out by Adamek et al., Canadian Journal of Chemistry, 35: 960 (1957). Stern, U.S. Patent No. 1,412,020, prepared wood glues in which up to 10 percent of very highly substituted starch Xanthate was added to either starch paste or to cellulose Xanthate and then was partially crosslinked by air om'dation. Also Elssner, US. Patent No. 2,000,887, reduced the luster of rayon by adding about 10 percent of an earth metal salt of a highly substituted starch Xanthate to a cellulose Xanthate spining solution. Meadows, US. Patent No. 2,741,247, teaches the addition to soil of 0.0l0.l percent by weight of uncrosslinked cellulose xanthate or starch xanthate as a soil conditioning agent and suggests the Xanthation of other polysaccharide materials such as dextrins, dextrans, agar, seed hulls, wheat, and corn for the above purposes. Schur, US. Patent No. 1,905,757, teaches the oxidative destruction of odor in pap-er containing up to one percent viscose.

it appears that no one heretofore has seriously considered preparing paper pulps and paper products in which a substantial portion of the cellulosic fibers is efiectively replaced by a cereal pulp as herein defined. If such cereal pulp containing papers were ever contemplated, it is apparent that the thought would have been discouraged by the prior art knowledge that when other starch derivatives are incorporated in paper at levels higher than about 3 to 4 percent the paper is stiffened and its fold endurance is very adversely afiected. Moreover, in Wet-end addition, prior art starches must be added in impraoticaily high amounts and under impractical operating conditions in order to incorporate more than about 3 to 4 percent starch product in the finished paper. Even with cationic starches which, compared to other prior art starches, have relatively good substantivity for cellulosic fibers, addition oi a suficient amount at the wet-end to achieve a 3 to 4 percent level of incorporation results in a sticky, slowdraining, unmanageable pulp. To the contrary, in the discoveries of the instant invention, we have now surprisingly found that paper and paperboard products having superior properties including increased wet-strength are easily obtained from combination pulps in which from at least about 4 percent and up to about 50 percent of the heretofore substantially exclusive cellulosic fiber content of the paper product has been replaced through the addition of a nominal excess above the desired replacement percentage of a cereal or carbohydrate alkali Xanthate that is then crosslinked in situ at the wet-end before sheet formation to become constituent cereal pulp as above defined and yield partially nonfibrous paper products, that contain from a modest proportion up to about 2:) much of the cereal pulp as they contain cellulose .The foregoing general description of our invention makes it apparent that our discoveries afiord the paper industry the conserving advantages of a novel and uniquely advantageous class of inexhaustibly available extenders or partial substitutes for the relatively diminishing domestic softwood pulp resources and at the same time ofiers a sorely needed opportunity for the development of significantly large new markets for cereal grain products.

Accordingly, a principal object of this invention is the Patented Dec. 8, 1964 preparation of eellulosic pulp-cereal pulp blends comprising at least about 4 percent based upon the dry weight of cellulose fibers and up to about 100 percent thereof of a cereal pulp material such as CIOSSllIlkSd xanthates of a cereal flour such as Whole wheat, bran, or refined white flour, or a crosslinked xanthate of such polysaccharides as starch, cellulose, dextrin, dextran, or guar gum, or a crosslinked xanthate of other polyhydroxy compounds such as' polyvinyl alcohol.

A further object is the in situ crosslinking of the aforesaid xanthates to form cereal pulps that are firmly bonded to the cellnlosic fibers which on conventional machines can then be made into paper and paper products, or into fibertype board, or boxboard having a greatly diminished cellulose fiber content and containing the said cereal pulp material in an amount replacing the sharply lowered ceilulosic fiber content.

Yet another object is the preparation of paper and pressed wood or fiberboard comprising greatly reduced proportions of wood pulp and ground wood.

A still further object is the preparation of partially nonfibrous paper products having unexpectedly improved tensile strengths.

A very specific object is the preparation of strong greaseproof-type paper.

A still further object is a method for increasing the freeness and water-drainage or greaseproof-type and conventional cellulose pulp slurries.

The above and additional objects will be made clearer in the course of the following nonlimiting examples and claims.

EXAMPLE 1 Two hundred grams of wheat starch (9.59 percent moisture) was slurried in 200 ml. carbon disulfide and 200 ml. of 18 percent potassium hydroxide solution was added thereto with stirring. With occasional further stirring the slurry was allowed to stand for 3 hours at room temperature. The starch x-anthate product was then washed in a 5-percent solution of acetic acid in methanol, dried, and pulverized before washing again in a S-percent solution of acetic acid in methanol. Then it was washed in anhydrous methanol and finally in diethyl ether before drying in vacuo over calcium chloride. The degree of substitution of the potassium starch xanthate powder obtained was about 1.0 xanthate groups per anhydroglucose unit in the starch.

To 15 grams samples of unbleached softwood sulfate pulp (Schopper-Riegler (S-R) freeness of 700 ml.) suspended by mechanical stirring in 4,000 ml. of water were added 2 percent rosin and 4 percent alum, based on the dry weight of cellulose fiber, along with either none of the potassium starch xanthate (control) or an amount equivalent to the addition of 50 parts of starch per 100 parts of dry cellulose fiber. The xanthate group present in the potassium starch xanthate was oxidatively crosslinked in situ by adding a slight excess of 1 N iodine solution to give the insoluble disulfurdicarbothionate product intimately bonded with the cellulose fibers. The excess iodine was then destroyed with sodium thiosulfate solution and the pH of the slurry was adjusted from its value of 6.8 to 5.2 with hydrochloric acid before preparing replicate handsheets, the physical data for which are set forth in Table I. It will be observed that much higher amount of starch in the form of cereal pulp was incorporated into the paper than could be incorporated with the prior art additions and that improvements in both wet strength and dry strength were obtained even at this high level of incorporation.

Although the mechanism by which the crosslinking induces bonding to the cellulose fibers is not entirely understood, we have determined that the crosslinking reaction occurs exclusively through the dithiocarbonate groups of the xanthate, converting these labile groups into stable groups. Thus, there are no free dithiocarbonate groups 4 present to greatly reduce the stability of the products as would be the case if crosslinking were effected through residual hydroxyl groups of the xanthate by employing crosslinking agents such. as diisocyanates.

Fifty parts by weight of wheat starch (10.88 percent moisture) were slurried in 63 parts of carbon disulfide and mixed with 120 parts of 18 percent aqueous sodium hydroxide. After standing for 3 hours with occasional mixing, the sodium starch xanthate was dissolved by adding water to give a final concentration of 2.97 grams per 100 ml. The sodium starch xanthate had a D.S. of about 0.7, and this solution which was oxidized to the disulfurdicarbothionate compound with iodine gave a product containing 16.79 percent sulfur, which corresponds to a disul-furdicarbothionate having a D.S. of 0.52.

A second solution was prepared in the same way but the starch was slurried in 6.3 parts of carbon disulfide that was diluted with 40 parts of benzene. The sodium starch xanthate had a D.S. of 0.35 and upon oxidation with iodine gave a starch disulfurdicarbothionate having a sulfur content of 7.38 percent and a final D.S. of 0.21.

The above sodium starch Xanthate solutions were added to 15 parts of unbleached softwood sulfate pulp, S-R freeness of 700 ml., suspended in 4,000 parts of tap water at respective addition levels corresponding to 4, 40, and parts of ori inal unmodified starch per parts of dry cellulose fiber for the specific xanthate of D.S. 0.35 and 40 and 80 parts of starch per 100 parts of dry cellulose fiber for the xanth-ate of D.S. 0.7. In no case were any other additives used.

Crosslinking to form the disulfurdicarbothionate compound was accomplished using a slight excess of iodine solution and stirring 30 minutes. Excess iodine was destroyed with a minimum amount of sodium thiosulfate. The pH values were controlled during crosslinking and each final slurry had a pH near 7.5. Handsheets prepared from the above are evaluated in Table II. Pronounced improvements in dry strength and greatly improved wet strength properties of the handsheets were obtained. From the percent cereal pulp in the paper it is calculated that at the highest levels of addition, nearly quantitative incorporation of the starch in finished paper occurred.

TABLE 11 Physical properties of Level of hand sheets addition D.S. of di- Percent by as starch sullurdiweight equivalent earbocereal pulp Breaking length in meters thionate in paper Dry Vet None 7, 600 220 O. 21 1. 8, 520 770 0.21 18. 7 9, 500 1, 600 O. 21 40. 4 8, 520 1, 570 0. 52 19. 6 8, 650 880 0. 52 45. 0 6, 770 970 EXAMPLE 3 the starch xanthates were dissolved in water to give solutions containing 4.0 percent by weight, dry starch basis. The viscosity of these 4 percent solutions was measured, and the D5. of the starch Xanthates was determined.

Xanthated to a degree suificient to give upon oxidative crosslin-king with iodine a disulfurdicarbothionate having a sulfur content of 4.72 percent.

Each of these Xanthates was added to unbleached sulfate TABLE III 5 softwood pulp (S-R freeness 700 ml.), in an amount sodium corresponding to the addition of 10 parts of wheat flour hydroxide or bran flour per 100 parts of dry cellulose fiber at the 5 3 Eggfig? fil'gf chest of a small Fourdrinier papermachine, with Concenstarch cps. stirring, and then oxidatively crosslinked in situ as pre- Moles (i i 3 31 1 12 10 viously described. These disulfurdicarbothionate-conp taining pulps ran on the machine as well as a control run 2 l5 1 2 495 M5 using the same pulp without the additive and gave paper riggggnu (1)5 3 1 5 1 ggg 8.3% having greatly improved wet tensile strength and conl 2 2 Q9 siderably improved bursting strength as shown 1n Table V. os309 0.2 4.3 1 0.2 30 0. 05 5 TABLE V Each of these solutions was added to a suspension of Physical p pe t e o bleached softwood sulfate pulp (S-R ireeness 700 1111.), Level Percent by paper containing gnams of pulp per 4,000 1111., at levels of addition, p we g t addition corresponding to the addition of 5 or 50 parts of Addmve used g g igif iiig ih Burst i ri i riitiai s starch per 100 parts of dry cellulose fiber. Then the equivalents p p factor starch Xanthate was oxidatively crosslinked in situ with Dry Wet the pulp by bubbling chlorine gas slowly into the suspension while stirring and controlling its pH between 5.5 and None (pulp 7.0. Properties of paper handsheets prepared firom these t lh- 0 0 43 9,480 350 pulp furnishes are given in Table IV. filfiffff 1.0 7.0 46 8,730 1,350 TABLE IV Wheat bran pulp 10 as 46 8,900 1,980

Physical properties of handsheets Starch xanthate item CS. 376 of Example 3, was used 3D in experiment that shows a method for greatly improvga g gg gfi Breakinglength ing the process of greaseproof paper manufacture. The tion as starch cereal pulp Schopper Burst in meters starch xantnate was added in an amount corresponding to equivalent m paper ggg actor 50 parts of starch per 100 parts of dry cellulose fiber to a Dry Wet dilute suspension containing 0.375 percent, of a partially hydrated, bleached softwood sulfite pulp having an S-R Control, None ,0 57 8,030 230 freeness of 500 ml. Chlorine gas was then added to ef- CS3G8: 28 1 220 68 9 610 500 feet in situ crosslinking. Handsheets prepared from g 6 giggg g: 28 this pulp were comparedwith those made from the un- Csss? n 5 56 529 1,000 treated pulp and irom a highly hydrated form of the same C3376, 24 040 66 3,840 Q2 control pulp which had been beaten enough to reduce the 6 50% n 25 2,310 8,300 S-R freeness from 500 ml. to 250 ml. This 250 ml. (S-R) ireeness pulp was satisfactory for making a paper of the The data in Table IV very clearly shows that a wide greaseproof type and was included in this example to range of desirable properties may be introduced int illustrate the very slow drainage and other properties of paper products thl'Ollgh this invention. By nsing various hydrated pulps ordinarily used in .greaseproof paper prolevels of addition and difierent starch xanthate preparative duction. The data of Table VI clearly shows that'the methods, advantages may be obtained including (1) re in situ crosslinking of the starch product according to placement of large amounts of wood pulp with the cereal the method of this invention provides a method of obtainpulp product While retaining or improving the Strength ing very free pulps for manutacture of greaseproof paper. properties of the paper product, particularly wet strength; The greaseproof paper produced by this method had suand (2) high retention of the starch disulfurdicarbothioperior transparency, folding endurance, wet strength, and nate in the finished paper even though the starch xanthate dry bursting strength. A more important advantage was is added as a beater or Wet-end additiv giving, bef r that it could be produced from a cheaper, less beaten pulp crosslinking, at a very great dilution of the starch xari- 7 having good freeness, allowing higher machine speeds thate solution. thereby giving great economic advantages.

TABLE VI Physical properties of handsheets Level of S-R addition Percent by freeuess of cereal weight Drainage Breaking Porosity, of pulp pulp as cereal time, length in sea/100 cc.

ml. starch pulp 111 sec. Opacity, Fold Burst meters equivalent paper percent Schopper factor Dry Wet None None 52 4s 2, 470 62 9,670 530 000+ None None 293 45 2,800 49 9, 040 880 600+ 50 23 30 30 4, 510 63 9,070 1,210 600+ EXAMPLE 4 EXAMPLE 6 Finely ground, hard red winter wheat flour (0.16 per- Xanthated starch giving starch disulfurdicarbothionate cent S, 2.42 percent N) was Xanthated to a degree snfliof BS. 0.14 was prepared and added to a highly hydrated cient to give a disulrurdicarbothionate upon iodine oxidacommercial greaseproof-ty-pe :pulp (bleached sulfite pulp) tion that contained 7.64 percent sulfur and 2.05 percent at a level of application (40 percent) sufiicient to give nitrogen. Wheat bran from hard red winter wheat was paper of 29 percent starch disulfurdicarbothionate con- 7!. tent as shown in Table VII on subsequent in situ crosslinking with iodine.

Addition of starch pulp to the highly hydrated sulfite pulp greatly improved drainage time of the latter and gave a greaseproof paper with considerably better transparency and wet strength than was obtained from the sulfite pulp alone.

8 EXAMPLE 8 An aqueous solution containing a starch xanthate of D5. 0.4 was prepared and aliquots of the solution added to two separate batches ofan 0.375 percent pulp furnish made from unbleached softwood pulp having an S-R freeness of 700 ml. The pH of the starch Xanthate pulp TABLE VII Physical properties of paper Percent by Level of addition weight Drainage of cereal pulp as cereal time, Breaking length starch equivalent pulp in sec. Burst in meters Opacity,

' paper factor percent Dry Wet None (0.1 222 control) None 107 37 7, 700 370 6 40% 29 36 39 7, 600 750 30 EXAMPLE 7 slurries was adjusted to 7.0 and the starch xanthate cross- Bleached white wood pulp, wheat flour, a canary dextrin, dextran, guar gum, polyvinyl alcohol, and sucrose were respectively Xanthated to suflicient degree to give on oxidative coupling disulfurdicarbothionates having the degrees of substitution shown in Table VIII. 'Xanthation was carried out as previously described except for the highly-substituted sucrose Xanthate which was prepared by reacting commercial sucrose, carbon dis-ulfide, and percent aqueous sodium hydroxide in a molar ratio of 1:5 :5. The resulting sucrose xanthate on addition of iodine was oxidatively polymerized and crosslinlzed to give a high polymer having the sucrose disulfurdicarbothionate unit a the repeating unit.

The above Xanthates were each added to 0.375 percent slurries of softwood unbleached sulfate pulp (S-R freeness 700 ml.) and the pH adjusted with 10 percent acetic acid solution to a value of 7.0 except for the sucrose Xanthate pulp slurry which was adjusted to pH 8.0. In situ crossliuking of the Xanthates was carried out with iodine as previously described.

Properties of paper handsheets prepared from these disulfurdicarbothionate containing pulp slurries are given in Table VIII. It will be noted that both high molecular Weight materials and the water soluble low molecular weight materials such as canary dextrins and sucrose when xanthated are retained to a high degree yet improve the strength properties of the paper, especially wet strength. This method of crosslinking in situ of xanthated hydroxy materials is not limited to the above types of materials; but can be potentially applied to any substance having more than two hydroxy groups, being capable of xanthation since, as shown in the case of sucrose, the reaction gives a method of coupling monomeric compounds to give polymeric compounds coupled in situ with the paper pulps.

TABLE VIII Percent Disulfurdi- Physical properties of earbothionate paper Material from which disulfurdicarbothionate Breaking length was derived Percent by Burst in meters D.S weight in factor paper Dry Wet None (control pulp O.P.

239) 0 0 59 8, 680 290 Bleached sulfite pulp 0. 28 32 52 7, 030 1, 840 Bleached sulfite pulp (O.P. 12) 0. 11 S, 310 2, 740 0. 27 1G 66 8, 580 1, 400 0. 00 35 57 8, 630 1, 700 0. 46 20 63 S, 520 1, 550 0. O5 4 92 11, 900 2, 670 Sucrose 2. l 9 62 9, 150 870 linked in situ with either zinc ions or ferric ions in the form of a 10 percent solution of the chloride. Physical properties of the handsheets prepared from the resulting pulp slurries are given in Table IX. Paper containing the zinc dithiocarbonate of starch was lighter in color and more opaque than the control whereas a decorative mahogany color was imparted to the paper by the iron coupled-cereal pulp product. The crosslinked product or starch pulp formed with zinc ions is a zinc clithiocarbonate of starch whereas, with ferric ion, oxidation probably occurs to yield a mixture of disulfurdicarbothionate of starch and the ferrous dithiocarbonate of starch.

25 g. portions of cellulosic fibrous materials including bleached sulfite softwood pulp, unbleached kraft pulp,

.hardwood sulfate pulp, ground wood, commercial ground corncobs, and whole ground kenaf plants (to pass a 2.5 mm. mesh screen) each suspended in 700 ml. of water. Upon crosslinking, the starch Xanthate with iodine in the usual manner, the starch disulfurdicarbothionate was intimately deposited upon the cellulose fibers. The starch 'disulfurdicarbothionate-cellulosic fibrous material was treated with sodium thiosulfate to destroy excess iodine, recovered by filtration, washed in conventional manner, and dried to about 10 percent moisture content. The above materials were compression molded at C. and 4,000 p.s.i. pressure for 5 minutes to give strong, smooth-surfaced discs that could be cut like wood with a knife. Physical test data for these products are given in Table X.

tarch xanthate was prepared similarly to C8368 of Table III, using 0.5 mole each of carbon disulfide and sodium hydroxide per mole of wheat starch. The Brookfield viscosity of a 4.0 percent solution of this Xanthate was 1,180 centipoises, and its Xanthate B5. was 0.15.

This starch Xanthate was added to a suspension of 15 grams of ground wood in 4,000 ml. of tap water at an addition level high enough to give 4 percent by weight of starch disulfurdicarbothionate in the finished paper product. Then the starch xanthate was crosslinked by carefully bubbling chlorine gas into the stirred ground wood suspension while controlling the pH between 5.5 and 7.0. Paper handsheets were formed from this pulp furnish and their physical properties were determined. As controls, paper hmdsheets were made from ground wood alone and from blends of ground wood with 9 percent and with 16 percent long-fibered bleached softwood sulfate pulp having an S-R freeness of 700 ml. The physical properties of the paper hand sheets are given in Table XI. ln the commercial production of newsprint papers, it is necessary to add long-fibered wood pulps, such as a bleached softwood sulfate pulp, to the ground wood furnish in order to give the paper web a high enough wet-web strength to allow its formation at high speeds on Fourdrinier machines. The long-fiber also increases the dry tensile strength of the newsprint to make possible the high speed printing of newspapers and similar publications. Table XI clearly shows that the addition of only 4 percent of the in situ formed starch pulp gives a newsprint product having improved burst and dry and wet tensile strengths over a newsprint product containing even as much as 16 percent of expensive long-fibered refined wood pulp. This substitution of cheap cereal products for expensive high grade refined wood pulps could clearly beimportant economically in newsprint production.

Amylose xanthate was prepared by reacting one mole of corn amylose (92.0 percent amylose, intrinsic viscosity 1.07) with one mole each of sodium hydroride and caramylose Xanthate was diluted with water to give a 9.8 percent solution, on a dry amylose basis. The Xanthate B5. was 0.4.

A clay coating for paper Was prepared using 20 parts of this amylose xanthate solution (on a dry amylose basis) as adhesive to parts of clay and containing 35 percent total solids. On the basis of the aforesaid proportions and as calculated therefrom, the resulting aqueous dispersion contained, per 100 ml. thereof, about 5.83 percent, on a dry weight basis, of sodium amylose Xanthate (derived from said 92.0 percent amylose and having said Xanthate degree of substitution of about 0.4) and about 29.17 percent, by weight, of clay. It was applied to paper, then exposed to a chlorine gas atmosphere for 15 seconds, to crosslink the amylose through formation of disulfurdicarbothionate linkages. The resulting clay coated paper, prepared by in situ crosslinking of its adhesive after application of the coating to the paper, was tested for wet-rub resistance and Wax pick value in the conventional way. The wet-rub resistance of the coating containing cereal pulp as the adhesive was superior to clay coatings containing an ordinary starch adhesive and about equal to clay coatings containing formaldehyde cured casein adhesive. The cereal puip coating had a Dennison wax pick value of 9 but as this was obtained the body stock of the paper ruptured showing that the coating adhered to the paper with a strength greater than the internal cohesive strength of the paper sheet itself.

Having disclosed our invention, we claim:

1. A pulp slurry for making a paper product comprising an aqueous dispersion of softwood fibers and about from 1% to 100%, based on the dryweight of the softwood fibers, of an oxidatively crosslinked Xanthate of a member selected from the group consisting of cereal flour, starch, cellulose, guar gum, dextran, dextrin, sucrose, and polyvinyl alcohol, said crosslinked Xanthate having been formed in situ in the presence of the softwood fibers from the corresponding non-crosslinked xanthate having a xanthate degree of substitution of about from 0.05 to 1.0 and being uniformly distributed among and intimately bonded to the softwood fibers.

2. A pulp slurry for making greaseproof paper comprising an aqueous dispersion of bleached softwood fibers that have been hydrated to a Schopper-Riegler freeness of 500 ml. and about 50%, based on the dry weight of the softwood fibers, of an oxidatively crosslinked sodium starch Xanthate which was formed in situ in the presence of the softwood fibers from the corresponding noncrosslinked sodium starch Xanthate having a Xanthate degree of substitution of about 0.09 and which is uniformly distributed among and intimately bonded to the softwood fibers.

3. A pulp slurry for making a wood substitute comprising an aqueous suspension of substantially equal amounts of a fibrous cellulosic material selected from the group consisting of ground wood, ground corncobs, ground kenaf, bleached sulfite pulp, hardwood sulfate pulp, and unbleached kraft pulp and an oxidatively crosslinked potassium starch Xanthate which was formed in situ in the presence of the fibrous cellulosic material from the corresponding non-crosslinked potassium starch xanthate having a Xanthate degree of substitution of about 0.5 and which is uniformly distributed among and intimately bonded to the cellulose fibers of said fibrous cellulosic material.

4. A process of making a paper product comprising forming an aqueous pulp slurry containing a dispersed cellulosic fibrous material and about from 1% to 100%, based on the dry weight of the cellulosic fibers, of a Xanthate of a member selected from the group consisting of cereal flour, starch, cellulose, guar gum, dextran, dextrin, sucrose, and polyvinyl alcohol, said Xanthate having a Xanthate degree of substitution of about from 0.5

to 1.0, subjecting the aqueous pulp slurry to the action of an oxidative crosslinking agent selected from the group consisting of iodine, chlorine, zinc chloride, and ferric chloride to form a modified pulp wherein the Xanthate has been oxidatively crosslinked in situ in the presence of the cellulosic fibrous material and the thus-crosslinked xanthate uniformly distributed among and intimately bonded to the cellulose fibers of the cellulosic fibrous material, and manufacturing a paper product from said modified pulp.

5. A method for making greaseproof paper comprising forming an aqueous pulp slurry containing dispersed bleached softwood fibers that have been hydrated to a Schopper-Riegler freeness of 500 ml. and about 50%, based on the dry weight of the softwood fibers, of a sodium starch Xanthate having a Xanthate degree of substitution of about 0.09, subjecting the aqueous pulp slurry to the action of an oxidative crosslinlring agent selected from the group consisting of iodine, chlorine, and zinc chloride to form a modified pulp wherein the sodium starch xanthate has been oxidatively crosslinked in situ in the presence of the softwood fibers and the thus-crosslinked xanthate is uniformly distributed among and intimately bonded to the softwood fibers, and manufacturing greaseproof paper from the modified pulp.

6. A method of making a wood substitute comprising uniformly suspending in an aqueous medium substantially equal parts, on a dry weight basis, of a fibrous cellulosic material selected from the group consisting of ground wood, ground corncobs, ground kenaf, bleached sulfite pulp, hardwood sulfate pulp, and unbleached kraft pulp, and a potassium starch Xanthate having a Xanthate degree of substitution of about 0.5, subjecting the resulting aqueous pulp slurry to the crosslinking action of iodine to form a modified pulp wherein the xanthate has been oxidatively crosslinked in situ in the presence of the fibrous cellulosic material and the thus-crosslinked xanthate uniformly distributed among and intimately bonded to the cellulose fibers of the cellulosic fibrous material, treating this modified pulp with sodium thiosulfate to destroy excess iodine, filtering the modifiedpulp to remove free water, washing the modified pulp, drying it to a moisture content of about 10%, and molding it at a temperature of about 130 C. under a pressure of about 4000 p.s.i.g. for about minutes to obtain a molded product suitable as a Wood substitute.

7. The process of claim 6 wherein the fibrous cellulosic material is bleached sulfite pulp.

8. A process for making paper having high wet-rub resistance comprising coating paper with an aqueous dispersion containing per 100 ml. thereof about 5.83 percent, on a dry weight basis, of sodium amylose Xanthate derived from amylose having a purity of 92% and a xanthate degree of substitution of about 0.4 and about 29.17% by weight of clay, exposing the coated paper to a chlorine gas atmosphere to oxidatively crosslink the sodium amylose Xanthate in situ in the presence of the paper, and drying the thereby treated and coatedpaper.

9. Paper, characterized in that it possesses both high dry and wet tensile strength, consisting essentially of about from 1.6% to 45% of its total weight of an in situ oxidatively crosslinked Xanthate of a member selected from the group consisting of cereal flour, starch,

cellulose, guar gum, dextran, dextrin, sucrose and polyvinyl alcohol, the remainder of the paper consisting essentially of cellulosic fibers, said crosslinked xanthate having been formed in situ in the presence of the cellulosic fibers from the corresponding non-crosslinkedxanthate having a xanthate degree of substitution of about from 0.05 to 1.0 and being uniformly distributed among and intimately bonded to said cellulosic fibers.

10. Grease proof paper consisting essentially of about 23% of its total weight of an insitu oxidatively crosslinked sodium starch Xanthate, the remainder of the paper consisting essentially of bleached softwood fibers that had been hydrated to a Schopper-Riegler freeness of 500 1111., said crosslinked xanthate having been formed in situ in the presence of the softwood fibers from the corresponding non-crosslinked sodium starch xanthate having a xanthate degree of substitution of about 0.09 and being uniformly distributed among and intimately bonded to said bleached softwood fibers.

11. A wood substitute consisting essentially of about from 26% to 48% of its total weight of an in itu oxidatively crosslinked potassium starch Xanthate, the remainder of the wood substitute consisting essentially of a cellulosic fibrous material selected from the group consisting of ground wood, ground corncobs, ground kenaf, bleached sulfite pulp, hardwood sulfate pulp, and unbleached kraft pulp, said crosslinked potassium starch xanthate having been formed in situ in the presence of the cellulosic fibrous material from the corresponding non-crosslinked potassium starch xanthate having a xanthate degree of substitution of about 0.5 and being uniformly distributed among and intimately bonded to the cellulose fibers of said cellulosic fibrous material, said wood substitute being in a molded form attained by compression at about 130 C. and about 4000 p.s.i.g. for about 5 minutes.

12. The wood substitute of claim 11 wherein the cellulosic fibrous material is bleached sulfite pulp.

13. Paper, having high wet-rub resistance, comprising paper coated with a composition containing an oxidatively crosslinked sodium amylose xanthate and clay in the proportion of about 20 parts, on a dry weight basis, of the oxidatively crosslinkecl sodium amylose xanthate per parts by weight of the clay, said oxidatively crosslinked sodium amylose xanthate having been produced in situ in the presence of the paper by exposing sodium amylose xanthate having a xanthate degree of substitution of about 0 .4 to a chlorine gas atmosphere.

References Cited by the Examiner UNITED STATES PATENTS 1,680,020 8/28 Harrison 260233.5 1,745,557 2/30 Richter et al l62177 1,820,962 9/31 Clapp 1 62--l77 1,856,114 5/32 Richter etal 162--177 1,905,757 4/33 Schur 162177 2,736,652 2/56 Novak 162175 2,825,655 3/58 Meadows 260233;5 2,900,268 4/59 Rankin at al. 260233.3

DONALL H. SYLVESTER, Primary Examiner.

MORRIS O. WOLK, Examiner. 

1. A PULP SLURRY FOR MAKING A PAPER PRODUCT COMPRISING AN AQUEOUS DISPERSION OF SOFTWOOD FIBERS AND ABOUT FROM 1% TO 100%, BASED ON THE DRY WEIGHT OF THE SOFTWOOD FIBERS, OF AN OXIDATIVELY CROSSLINKED XANTHATE OF A MEMBER SELECTED FROM THE GROUP CONSISTING OF CEREAL FLOUR, STARCH, CELLULOSE, GUAR GUM, DEXTRAN, DEXTRIN, SUCROSE, AND POLYVINYL ALCOHOL, SAD CROSSLINKED XANTHATE HAVING BEEN FORMED IN SITU IN THE PRESENCE OF THE SOFTWOOD FIBERS FROM THE CORRESPONDING NON-CROSSLINKED XANTHATE HAVING A XANTHATE DEGREE OF SUBSTITUTION OF ABOUT FROM 0.05 TO 1.0 AND BEING UNIFORMLY DISTRIBUTED AMONG AND INTIMATELY BONDED TO THE SOFTWOOD FIBERS.
 6. A METHOD OF MAKING A WOOD SUBSTITUTE COMPRISING UNIFORMLY SUSPENDING IN AN AQUEOUS MEDIUM SUBSTANTIALLY EQUAL PARTS, ON A DRY WEIGHT BASIS, OF A FIBROUS CELLULOISE MATERIAL SELECTED FROM THE GROUP CONSISTING OF GROUND WOOD, GROUND CORNCOBS, GROUND KENAF, BLEACHED SULFITE PULP, HARDWOOD SULFATE PULP, AND UNBLEACHED KRAFT PULP, AND A POTASSIUM STARCH XANTHATE HAVING A XANTHATE DEGREE OF SUBSTITUTIONS OF ABOUT 0.5 SUBJECTING THE RESULTING AQEUOUS PULP SLURRY TO THE CROSSLINKING ACTION OF IODINE TO FORM A MODIFIED PULP WHEREIN THE XANTHATE HAS BEEN OXIDATIVELY CROSSLINKED IN SITU IN THE PRESENCE OF THE FIBROUS CELLULOSIC MATERIAL AND THE THUS-CROSSLINKED XANTHATE UNIFORMLY DISTRIBUTED AMONG AND INTIMATELY BONDED TO THE CELLULOSE FIBERS OF THE CELLULOSIC FIBROUS MATERIAL, TREATING THIS MODIFIED PULP WITH SODIUM THIOSULFATE TO DESTROY EXCESS IODINE, FILTERING THE MODIFIED PULP TO REMOVE FREE WATER, WASHING THE MODIFIED PULP, DRYING IT TO A MOISTURE CONTENT OF ABOUT 10%, AND MOLDING IT AT A TEMPERATURE OF ABOUT 130*C. UNDER A PRESSURE OF ABOUT 4000 P.S.I.G. FOR ABOUT 5 MINUTES TO OBTAIN A MOLDED PRODUCT SUITABLE AS A WOOD SUBSTITUTE.
 8. A PROCESS FOR MAKING PAPER HAVING HIGH WET-RUB RESISTANCE COMPRISING COATING PAPER WITH AN AQUEOUS DISPERSION CONTAINING PER 100 ML. THEREOF ABOUT 5.83 PERCENT, ON A DRY WEIGHT BASIS, OF SODIUM AMYLOSE XANTHATE DERIVED FROM AMYLOSE HAVING A PURITY OF 92% AND A XANTHATE DEGEEE OF SUSTITUTION OF ABOUT 0.4 AND ABOUT 29.17% BY WEIGHT OF CLAY, EXPOSING THE COATED PAPER TO A CHLORINE GAS ATMOSPHERE TO OXIDATIVELY CROSSLINK THE SODIUM AMYLOSE XANTHATE IN SITU IN THE PRESENCE OF THE PAPER, AND DRYING THE THEREBY TREATED AND COATED PAPER. 